1. Field of the Invention
The invention concerns an optical sensor for measuring the property of a gaseous or liquid medium, particularly the opaqueness of a washing or rinsing liquid in a washing or rinsing machine, with at least one radiation source, a radiation receiver and a light-transmitting sensor body, with an optical boundary surface, which, depending on the nature of the medium present outside the boundary surface of the sensor body, to a greater or lesser degree transmits to the radiation receiver and/or reflects the radiation directed on to it, resulting at the radiation receiver in different measurement signals which characterise the reflectivity and the refractive index relationships at the boundary surface.
2. Description of the Related Art
An optical sensor of this type is known from the DE 42 42 927 A1. This known sensor has a single radiation source and a single radiation receiver and the different measurement signals are based on a combination of the physical effects of reflection and variation of the refractive index relationship at the boundary surface of the lens-type sensor body. The measurement signals permit differentiation in foam, air and liquid outside the sensor body. In this case only differentiation is effected by the measurement signal in the presence of water, air or foam. This optical sensor is not adequate for the purpose of determining unambiguously the opaqueness of the washing or rinsing liquid in a washing or rinsing machine since if the liquid is dirty to a greater or lesser degree the measurement signal obtained is essentially the same. Since differing dirtiness of the water is the single-valued criterion of the progress of the process cycle in a washing or rinsing machine and thus of sensor-controlled changing of the program, an optimum process control cannot be established with the known sensor.
It is therefore the object of the invention to create an optical sensor, of the type initially referred to, by means of which it is possible to derive unambiguously differentiable measurement signals for the degree of opaqueness of a liquid medium in a washing or rinsing machine which can be used for process control.
This object is achieved, according to the invention, in that an additional radiation source for detecting the transparency of the medium directs a radiation through the medium and the sensor body on to the radiation receiver and in that the radiation receiver emits in chronological succession the measurement signals which are initiated by the two time-multiplexed radiation sources and which characterise the transparency and reflection of the medium, or in that an additional radiation source for detecting the transparency of the medium directs a radiation through the medium on to an additional receiver and in that the two radiation receivers simultaneously emit the measurement signals which are initiated by the assigned radiation sources and which characterise the transparency and reflection of the medium.
The sensing of the transparency of the medium also measures its degree of opaqueness, so that different measurement signals, which can be used for process control, are obtained according to the degree of dirtiness. In the first case, the time multiplex operation means that only an additional radiation source is required, whereas in the second case parallel determinations are obtained concerning the reflectivity and transparency of the medium with the use of an additional radiation receiver. By contrast with the known optical sensor, therefore, in the case of water being present as a medium simultaneous differentiation is still possible in different degrees of dirtiness of the medium, this being of considerable advantage for control of the process, i.e., changing of the programs, for the purpose of optimising the process according to time, temperature, water and energy and adapting it to different conditions.
For the purpose of obtaining unambiguous measurement signals in measurement of the transparency, there is provision, according to one embodiment, whereby the radiation source for measuring the transparency of the medium directs the radiation through the medium, transversely relative to the direction of flow of the latter.
If the arrangement is such that the boundary surface of the lens-type sensor body faces towards the medium and forms a part of a light-transmitting sensor casing which itself forms a part of the channel through which the medium flows, and such that at least the boundary surface of the sensor body projects into the channel, then differentiation also occurs in the presence of air or foam.
The construction of the optical sensor is such that the sensor casing accommodates the radiation sources and the radiation receivers, the radiation source provided to detect the reflection of the medium and the single radiation receiver being disposed on the sensor body, facing away from the boundary surface of the sensor body, whereas the radiation source provided to detect the transparency of the medium and any additional radiation receiver provided for the latter are disposed outside the sensor body, in the sensor casing or in the channel.
If only a single radiation receiver is provided for detecting the transparency and the reflection of the medium, then, for the purpose of detecting the transparency, the optical sensor can be designed so that the sensor casing comprises in addition to the sensor body a chamber, projecting into the channel and the medium, in which is inserted the radiation source provided for detecting the transparency of the medium, which directs its radiation through the medium on to the boundary surface of the sensor body, or so that the sensor casing forms in addition to the sensor body a light guide, projecting into the medium and the channel, which deflects the radiation emitting from the radiation source for detecting the transparency of the medium and directs it through the medium on to the boundary surface of the sensor body.
The arrangement can also be designed so that the radiation source provided for detecting the transparency of the medium is disposed on the side of the channel opposite to the sensor body and so that the radiation emitting from this radiation source is directed through the sensor body on to the single radiation receiver.
The radiation sources are formed, most simply, by light-emitting diodes and the radiation receivers by phototransistors.